High resolving-power duplicating lens of unit magnification

ABSTRACT

A high resolving-power duplicating lens of unit magnification having the lens arrangement of longitudinal symmetry in which at the opposite ends of the center, negative meniscus lenses (I)(I) with the concave surfaces facing to the center, next to them positive lenses (II)(II) with the convex surfaces facing to the center, next to them lens groups (III)(III) consisting of two or more positive lenses, next to them negative meniscus lenses (IV)(IV) of doublets of which the concave surfaces nearest to the center are faced to the center, and a central double-concave lens (V) of singlet or multiplet symmetrical as a whole are so arranged as to satisfy the following conditions:

Kano

[5 1 HIGH RizsoLvmc-Powmt nurucxrmo LENS OF UNIT MAGNIFICATION [75]Inventor: lchiro Kano, Yokohama, Japan [73] Assignee: Canon KabushikiKaisha, Tokyo,

Japan [22] Filed: Jan. 13, 1972 [21] Appl. No.: 217,598

[30] Foreign Application Priority Data 181,- 0 v p n".f'jffff."'tt't'f7'if:f [52] U.S. Cl. 350/214 [51] Int. Cl. G02b 9/64 [58] Field ofSearch 350/214 [56] References Cited UNITED STATES PATENTS 2.481.6399/1949 Altman et a]. 350/214 X 3133.983 5/1964 Rickless et al 350/216 X2.836.100 5/1958 Richter et al. 350/214 X 3.540.800 ll/l970 Tibbetts etal 350/214 Primary Examiner-John K. Corbin Attorney. Agent. orFirm-Toren & McGeady [57] ABSTRACT A high resolving-power duplicatinglens of unit magnii new Mar. 19, 1974 fication having the lensarrangement of longitudinal symmetry in which at the opposite ends ofthe center, negative meniscus lenses (I)(l) with the concave suF facesfacing to the center, next to them positive lenses (lI)(lI) with theconvex surfaces facing to the center, next to them lens groups(lII)(lll) consisting of two or more positive lenses, next to themnegative meniscus lenses (lV)(lV) of doublets of which the concavesurfaces nearest to the center are faced to the center, and a centraldouble-concave lens (V) of singlet or multiplet symmetrical as a wholeare so arranged as to satisfy the following conditions:

where f focal length of each of the two blocks (A)(A) in air. into whichthe lens system is divided at the center d axial thickness of lens (IV)d distance between lens (II) and lens group (III) fy focal length oflens (V) 1 refractive index of the outside lens of lens (IV) 1refractive index of the inside lens of lens (IV) 1 Claim, 6 DrawingFlgures 1. HIGH RESOLVING-POWER DUPLICATING LENS OF UNIT MAGNIFICATIONThe present invention relates to a lens suitable for use in a case ofultrahigh resolving-power being necessary for the duplication of unitmagnification such as to produce integrated circuits by printingphotomasks on waters. The lens of this kind is required to have highresolving-power over an entire image field so that spherical aberration,coma aberration, astigmatism, curvature of image field, distortion, andoff-axis halo are necessary to be reduced to a high degree. It is knownthat the symmetrical arrangement of lenses is automatically free fromcoma and distortion. The present invention, employing the symmetricalarrangement of lenses, makes use of the above-mentioned feature toadvantage so that the aberrations which have to be reduced are sphericalaberration, astigmatism. curvature of image field and off-axis halo. Inthis case, it is the most difficult to reduce the field curvature andoff-axis halo simultaneously to a high degree. In general, as the fieldcurvature is made smaller, the off-axis halo tends to be reducedexcessively; as the off-axis halo is made smaller, the field curvaturetends to be reduced insufficiently. In addition, the tendency isparticularly remarkable in the symmetrical arrangement of lenses. Thepresent invention is to overcome this difficulty, and makes it possibleto correct for both the field curvature and off-axis halo to a highdegree by employing an arrangement which will be mentioned below.

The present inventive lens arrangement is of longitudinal symmetry, inwhich at the opposite ends of the center, negative meniscus lenses 1. Iwith the concave surfaces facing to the center, next to them positivelenses II, II with the convex surfaces facing to the center, next tothem lens groups III, III consisting of two or more positive lenses,next to them negative meniscus lenses IV, [V of doublets of which thesurfaces nearest to the center are concave surfaces facing to thecenter, and a central double-concave lens (V) of singlet or multipletsymmetrical as a whole are so arranged as to satisfy the followingconditions.

2. 02f, d, f,

f, focal length of each of the two blocks A, A in air, into which thelens system is divided at the center d axial thickness of lens IV :1,distance between lens II and lens group Ill 1% focal length of lens Vfin) refractive index of the outside lens of lens IV m refractive indexof the inside lens of lens IV The present invention will be described inreference to the attached drawings.

FIG. I is a block diagram of Example 1 of the present inventive lens,and FIG. 2 is a graph of aberration in case of the just-mentionedexample. FIG. 3 is a block diagram of Example 2 and FIG. 4 is a graph ofaberration in case of the just-mentioned example. FIG. 5 is a blockdiagram of Example 3 and FIG. 6 is a graph of aberration in case of thejust-mentioned example.

The present inventive lens belongs to a deformation of so-calledGauss-type lens. In the Gauss-type lens, in order to make fieldcurvature smaller, it is a good wav to increase the thickness of aconcave meniscus lens,

but this procedure results in an over-correction for offaxis halo. Inthe present inventive lens, concave meniscus lenses 1, I correcting forfield curvature without giving any influence to spherical aberration areplaced at the ends of the lens system, and therewithal the fieldcurvature is reduced to a high degree by increasing the thickness d ofconcave meniscus lens (lV)(lV) consisting of two cemented lenses to suchan extentas defined in condition 1. Where d is beyond this least upperbound, the tendency of over-correction for offaxis halo becomesstronger, accompaniedwith the insufficient correction for sphericalaberration. Where d is below this greatest lower bound, the effect onthe correction for field curvature cannot be expected.

Next, condition 2. is so defined as to compensate particularly themeridional halo out of the over-corrected off-axis halo occurring underconditions 1. Namely, as d, increases, on-axis ray passes through lensII at lower position, so that the refracting action of the convex lensdoes not work sufficiently. Therefore, in order to keep the focal lengthof lens block A constant, the refracting power of lens II should bestrengthened. On the other hand, off-axis principal ray passes throughlens II at higher position with the increase of 11., so that therefracting power of the convex lens affects it strongly, and, inaddition, lens Il itself becomes stronger in refracting power asmentioned before, thus the refracting action of the convex lens becominglarger. Therefore, this action compensates the off-axis meridional halofrom its over-correction in the direction to insufficient correction.However, as d, is increased too much, the refracting power of lens IIbecomes stronger than enough, so that the tendency of insufficientreduction for field curvature is strengthened and the overcorrection ofoff-axis sagittal halo becomes larger in contrast with the off-axismeridional halo. The least upper bound defines this limit, while belowthe greatest lower bound this correction effect cannot be obtained.

Next, condition 3. is so defined as to reduce the offaxis sagittal halo.If lens V is allowed to take over a portion of the negative refractingpower of lens I by strengthening adequately the negative refractingpower of lens V, the negative refracting power of lens I weakens. Inthis case, the over-correction for off-axis sagittal halo occurring atlens I diminishes. If the negative refracting power of lens V isstrengthened too much, the negative refracting power of lens I becomesso weak as to weaken the effect on correction for field curvature whichis the original object of that lens. The least upper bound of condition(3) defines the limit for obtaining the above-mentioned effect, whilebelow the greatest lower bound the effect cannot be obtained.

Next, condition 4. is so defined as to correct for the sphericalaberration. The spherical aberration is reduced to a high degree bycomposing the lens group III with two or more convex lenses andtherewith setting m n 0.01 for lens IV. The increase in number of lensesin'lens group III as such has an effect on the reduction of sphericalaberration, and, moreover, on setting mvr'mv 0.01, the negativerefracting power at th cemented surface of leris V is strengthened todecrease the quantity of insufficient correction for the sphericalaberration. If m n is increased too much. the excessive increase of thenegative refracting power at the cemented surface strengthens morestrongly the tendency of over-correction for the off-axis halo so that nn 0.2 is set so as to prevent this tendency.

matte "P5931.

lll

may be replaced with a double-concave lens of singlet.

Further, two lenses having the same refractive indices only for thereference ray and different refractive indices for other rays may becemented to make a doubleconcave lens symmetrical as a whole so as tocorrect for chromatic aberration.

What is claimed:

l. A high resolving-power duplicating lens of unit magnification havingthe lens arrangement of longitudinal symmetry in which at the oppositeends of the cen- 1 ter, negative meniscus lenses (I)(l) with the concavesurfaces facing to the center, next to them positive lenses (ll)(Il)with the convex surfaces facing to the center, next to them lens groups(lll)(lll) including a plurality of positive lenses, next to themnegative meniscus lenses (lV)(lV) of doublets of which the concavesurfaces nearest to the center face the center, and a centraldouble-concave lens (V) symmetrical as a whole arranged to satisfy thefollowing conditions:

where m z refractive index of the inside-lens of lens (lV).

l 0! k 1 l

1. A high resolving-power duplicating lens of unit magnification havingthe lens arrangement of longitudinal symmetry in which at the oppositeends of the center, negative meniscus lenses (I)(I) with the concavesurfaces facing to the center, next to them positive lenses (II)(II)with the convex surfaces facing to the center, next to them lens groups(III)(III) including a plurality of positive lenses, next to themnegative meniscus lenses (IV)(IV) of doublets of which the concavesurfaces nearest to the center face the center, and a centraldouble-concave lens (V) symmetrical as a whole arranged to satisfy thefollowing conditions:
 1. 0.57fA < dIV < 0.66fA
 2. 0.70fA < d4 < 0.73fA3. 0.15 < - (fA/fV) < 0.33
 4. nIV - nIV about .09 where fA : focallength of each of the two blocks (A)(A) in air, into which the lenssystem is divided at the center dIV : axial thickness of lens (IV) d4 :distance between lens (II) and lens group (III) fV : focal length oflens (V) nIV : refractive index of the outside lens of lens (IV) nIV :refractive index of the inside lens of lens (IV).
 2. 0.70fA < d4 <0.73fA
 3. 0.15 < - (fA/fV) < 0.33
 4. nIV - nIV about .09 where fA :focal length of each of the two blocks (A)(A) in air, into which thelens system is divided at the center dIV : axial thickness of lens (IV)d4 : distance between lens (II) and lens group (III) fV : focal lengthof lens (V) nIV : refractive index of the outside lens of lens (IV) nIV: refractive index of the inside lens of lens (IV).